This section describes the background of the disclosed embodiment of the present invention. There is no intention, either express or implied, that the background art discussed in this section legally constitutes prior art.
Photodiodes are used in a variety of applications. One application is for reading assay test strips, which may be used for testing samples for pregnancy, drugs of abuse, tobacco, or others. The photodiodes detect light intensity changes or color changes on the test strip for detecting the presence or absence of a substance in the test sample.
A conventional way, for some applications, of measuring the light intensity incident on two photodiodes is to use a microcontroller with two analog to digital (A/D) channels. Amplifiers may be needed for each photodiode channel to convert their very low current into a voltage that the A/D can measure. This technique may employ a relatively large number of components and is expensive to manufacture. Also, under certain circumstances, the dynamic range of measurement may be limited by the number of bits in the A/D converter.